The present invention relates to novel esters of phosphorous acid and phosphoric acid and to a novel method for their production. More particularly, the novel compounds are (halo)(hydroxy)-substituted phosphites and phosphorates characterized by a high hydroxyl number due to the method by which the compounds are produced.
In U.S. Pat. No. 3,939,227, the reaction between a halide of an alkyl phosphonic acid and a hydroxy terminated epoxy was reported. Specifically, the reference disclosed the reaction of glycidol with chloromethyl phosphonic dichloride. The reported product was a diol of the formula ##STR1## where R was chloromethyl; X was chloro; and a was 1. The compound was found to be a highly viscous material. No further characterizing data was supplied.
The method illustrated by the above reference has proven difficult in practice due to the competing reactions between hydroxyl, instead of the suggested epoxy moieties, with the active phosphorus reactant sites resulting in impure product and high molecular weight oligomers as indicated by the viscous nature of the reported product. It is, for example, well-known that phosphonic chlorides react only with great difficulty with epoxy groups unless a catalyst is employed, cf. U.S. Pat. Nos. 1,936,985; 2,610,978; 3,010,980; etc. Accordingly in U.S. Pat. No. 3,939,227, low temperatures were employed along with slow addition of the phosphorus compound to a dilute solution of the epoxide in order to limit, if possible, competing reactions of the hydroxyl moiety. This process is not commercially acceptable and, as previously explained, was not entirely successful in U.S. Pat. No. 3,939,227 in preventing contaminating reaction products as indicated by the highly viscous nature of the reported product. The highly viscous reaction product is unsuitable in many applications requiring a polyhydroxyl-containing compound having low hydroxyl equivalent weight.
Furthermore, the reaction technique of U.S. Pat. No. 3,939,227 is not amenable for use with more reactive phosphorus compounds such as POCl.sub.3, PCl.sub.3 or PCl.sub.5. The competing reaction of hydroxyl moieties with these more reactive phosphorus compounds readily forms undesirable reaction products.
Accordingly, it is an object of the present invention to provide a process whereby highly pure (halo)(hydroxy)alkyl phosphites and phosphorates may be prepared expeditiously and in high yield under commercially acceptable reaction conditions and times.
It is a further object of the present invention to produce highly pure (halo)(hydroxy)alkyl ester derivatives of phosphorus compounds of low viscosity suitable for use in producing polyurethanes by reaction with a diisocyanate-containing compound, said polyurethanes having flame-retarding characteristics. Preferably the (halo)(hydroxy)-substituted esters have a viscosity less than 500,000 centipoise at ambient temperatures in order that the compound be tractable and capable of use without employing a solvent.